The technology used in modern energy saving lighting devices uses mercury as one of the active components. As mercury harms the environment, extensive research is done to overcome the complicated technical difficulties associated with energy saving, mercury-free lighting.
An approach used for solving this problem is to use field emission light source technology. Field emission is a phenomenon which occurs when a very high electric field is applied to the surface of a conducting material. This field will give electrons enough energy such that the electrons are emitted (into vacuum) from the material.
In prior art devices, a cathode is arranged in an evacuated chamber, having for example glass walls, wherein the chamber on its inside is coated with an electrically conductive anode layer. Furthermore, a light emitting layer is deposited on the anode. When a high enough potential difference is applied between the cathode and the anode thereby creating high enough electrical field strength, electrons are emitted from the cathode and accelerated towards the anode. As the electrons strike the light emitting layer, typically comprising a light powder such as a phosphor material, the light powder will emit photons. This process is referred to as cathodoluminescence.
One example of a light source applying field emission light source technology is disclosed in EP1709665. EP1709665 disclose a bulb shaped light source comprising a centrally arranged field emission cathode, further comprising an anode layer arranged on an inside surface of a glass bulb enclosing the field emission cathode. The disclosed field emission light source allows for omnidirectional emission of light, which for example is useful in relation to a retrofit light source implementation.
Even though the EP1709665 shows a promising approach to a mercury free light source, the cathode structure used is relatively basic, specifically for achieving a high level of uniformity in regards to light emission. There is thus a desire to improve upon the cathode structure, thereby improving the overall impression of light emitted from the field emission light source. In addition, there is also a desire to present improvements in regards to a manufacturing method used for forming such a cathode, in particular concerning uniformity, controllability and repeatability.
Further attention is drawn to US2014346976 A1, relating to a method for manufacturing a plurality of nanostructures comprising the steps of providing a plurality of protruding base structures arranged on a surface of a first substrate, providing a seed layer mixture, comprising a solvent/dispersant and a seed material, in contact with the protruding base structures, providing a second substrate arranged in parallel with the first substrate adjacent to the protruding base structures, thereby enclosing a majority of the seed layer mixture between the first and second substrates, evaporating the solvent, thereby forming a seed layer comprising the seed material on the protruding base structures, removing the second substrate, providing a growth mixture, comprising a growth agent, in contact with the seed layer, and controlling the temperature of the growth mixture so that nanostructures are formed on the seed layer via chemical reaction in presence of the growth agent.
Further attention is also drawn to US2007284573 A1, relating to a process for fabricating ZnO nanowires with high aspect ratio at low temperature, which is associated with semiconductor manufacturing process and a gate controlled field emission triode is obtained. The process comprises providing a semiconductor substrate, depositing a dielectric layer and a conducting layer, respectively, on the semiconductor substrate, defining the positions of emitter arrays on the dielectric layer and conducting layer, depositing an ultra-thin ZnO film as a seeding layer on the substrate, growing the ZnO nanowires as the emitter arrays by using hydrothermal process, and etching the areas excluding the emitter arrays, then obtaining the gate controlled field emission triode.